Hi Dallas:
The only Uberti I have is a TG, BS, & Grip combination from an old Cattleman I once had.
The bluing has turned to a nice plum color.
I hate to break it up, cuz everything is fitted very well together.
But, I'll ship it to you for $80.
Paypal & Personal check is OK.
Please let me know.
Thanks
--Dawg

Generally accepted ball sizes have always been:
.451 for Piettas,
.454 for Ubertis,
,457 for Rugers.
Sounds to me like you are over-thinking this.
But, if you really want to measure each cylinder chamber.....
Seat a ball just below flush in each of your cylinder chambers
Drill a hole through it with a small bit.
Screw in a drywall screw, and put the cylinder in a vise.
Use pliers or vise grips to grab onto the screw head & pull the ball out.
Measure with calipers.
--Dawg

LR:
To be fair to everyone, we will not be accepting last years form, or forms that are sent in early.
Must be the current form which Bubba will put up on the Website on June 27th.
See y'all at High Noon 2020!
--Dawg

When it has happened to me, I have just put it on half-cock, and rotated the cylinder with my off-hand.
Honestly, I'm not sure about cocking & decocking to get the cylinder in the correct position, so I will watch this post to here what others (particularly Palewolf) have to say.
--Dawg

ACW:
I was not trying to derail your sale, but the fact that it is not a legal gun for Frontiersman should be known by any potential buyer.
I'm sorry if that upsets you, but imagine how the buyer would feel when he shows up at a match & finds out then.
It still would be a fun gun to have & shoot, just not in Frontiersman.
--Dawg

Shooter's Handbook. page 10:
Frontiersman Category Frontiersman Rules:
- Any main match percussion revolver with fixed sights.
- Revolvers must be shot Duelist or Double Duelist style. See Duelist description for required shooting technique.
- Must use blackpowder in all loads (rifle, revolver, and shotgun).
- Must use a side-by-side, single shot, or lever action shotgun in the main match stages.
- Any SASS legal pistol caliber rifle is acceptable.
Exceptions: - See “Sights” section of this handbook regarding “dovetail sights”
- The 1873 Uberti percussion revolver is not allowed.
Not trying to rain on your parade, but potential buyers should know that, even though this is a fixed sight cap gun, it is NOT LEGAL for frontiersman.
--Dawg